Steel-refining composition containing portland cement and fluorspar

ABSTRACT

A steel-refining agent which is composed of 35% to 65% of Portland cement, 5% to 20% of fluorspar, 20% to 40% of Chamotte powder, 2% to 15% of soda ash, 2% to 15% of a carbon source, which is coke breeze or graphite powder, and further 2% to 15% of borax, wherein more than 50% of mixing particles have a diameter of less than 0.044 mm.

AU 112 EX United States Patent STEEL-REFINING COMPOSITION CONTAINING PORTLAND CEMENT AND FLUORSPAR 6 Claims, 1 Drawing Fig.

lnt. Cl C22b 9/10 Field of Search 75/96; 106/97; 148/26 [56] References Cited UNITED STATES PATENTS 2,126,786 8/1938 Laoch et a1 75/96 X 2,728,681 12/1955 106/97 3,181,959 5/1965 106/97 X 3,376,146 4/1968 106/97 3,516,821 6/1970 75/96 253,158 l/1882 Campbell 75/96X FORElGN PATENTS 137,925 7/1950 Australia 106/97 22,519 1910 Great Britain.... 106/97 217,343 6/1924 Great Britain 106/97 Primary Examiner-Allen B. Curtis Attorney-Flynn& Frishauf I ABSTRACT: A steel-refining agent which is composed of 35% to 65% of Portland cement, 5% to 20% offluors ar, 20% to 40% of chamqg gpmer, 2% m 15% of 5011 5 2% to 15% of a carbon source, which is coke breeze or raphite powder, and further 2% to 15% of borax, wherein more than 50% of mixing particles have a diameter of less than 0.044 mm.

BACKGROUND OF THE INVENTION This invention relates to a novel steel-refining agent which is added into mold wherein liquid steel is cast and more particularly is east continuously.

While steel is cast by a bottom pouring method the surface of the molten steel poured into the mould is oxidized by the atmosphere. To avoid this oxidation it is common to cover the surface of the molten steel with straw ash or other heat-insulating material. Also in case of continuous casting, similar problems is brought about. Thus, it is well known that stream of said molten steel poured into a mold from a tundish and surface of said molten steel in said mold is subjected to oxidation caused by the atmosphere. Oxides of iron and deoxidizing element, especially aluminum oxides in case of aluminum killed steel not only tend to clog a nozzle of said tundish but also are entrained in the molten steel as contaminants to degrade the quality of the steel produced. And further, these oxides cause leakage of said molten steel which will bring forth the biggest difficulty of continuous casting process.

SUMMARY OF THE INVENTION It is an object of this invention to provide a novel steel refining agent which can effectively prevent oxidation of said liquid steel surface in an ordinary mold or a continuous casting mould and can absorb and remove some nonmetallic inclusions such as silica, aluminum or the like when flw these inclusions reach the surface of said liquid steel.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing, a single FIGURE illustrates a cross section of a portion of a continuous casting device to show a relation between the surface of slag formed by the steel refining agent and a pouring nozzle, where the steel-refining agent is added into the continuous casting mould.

DESCRIPTION OF THE PREFERRED EMBODIMENTS From the standpoint of technical view, such steel-refining agent must satisfy following requirements:

1. It can readily and quickly melt when contacted with the molten steel.

2. As soon as melted, it can quickly spread over the surface of liquid steel to prevent the surface from contacting the atmosphere.

3. When melted by the molten steel it must have a suitable viscosity to spread over the surface of liquid steel.

4. It does not impair properties of steel.

5. If desired, it can readily react with such nonmetallic inclusions in liquid steel as silica, alumina or the like, and remove these impurities.

6. In the case of continuous casting process, it can not only cover the surface of liquid steel but also form a thin film of slag between inside wall of said mold steel and formed slab to prevent rapid cooling of said slab. This is especially important to prevent occurrence of surface cracks of slab having width or more than 1200 mm.

7. It must be inexpensive.

To meet these requirements the novel steel-refining agent is characterized by the following composition, grain size and chemical and physical properties.

l. Mixing agent:

Portland cement 3510 Fluorspar (CAR) 5 0 20'1 Chamotte powder 20 to 40% Soda ash Z to lSZ Source of carbon including graphite powder or coke breeze O to 151 Borax 2 to l5 2. Grading distribution:

The percentage of particles having diameters of less than 0.44 mm. should be more than 50 percent. 3. The refining agent should have a melting point of from 1,000 to l,300 C., and a viscosity of 000 o IO pgises when melted by liquid steel.

The purpose of adding borax to the steel-refining agent of this invention is to lower the melting point of said agent to effectively prevent oxidation of the surface of said liquid steel This is especially desirable for some kinds of steel, for example killed steel.

The steel-refining agent of this invention is utilized in the following manner:

It is possible to employ the above agent in bottom pouring process. For example, the novel refining agent in an amount of 0.2 to 2.5 kg. per ton of the molten steel is packed in bags of paper of synthetic resin and these bags are placed in the bottom of a mold or hung therein by means of fine metal wires. When the liquid steel is poured into the mould through a runner brick to come into contact with said bags, the bags are burned to spread the refining agent over the surface of rising liquid steel. A melting point of the steel refining agent ranges from l,00O to 1,300 C. whereas the temperature of the molten steel is commonly more than 1,300 C., the refining agent will be melted quickly to readily cover the surface of said liquid steel. Since the refining agent has a property of forming slag as flotation of nonmetallic inclusions in liquid steel bath reaches the refining agent slag, said inclusions readily react with a slay layer and adsorbed thereby.

Where the novel steel-refining agent is utilized to cast killed steel ingots by the bottom pouring method it is able to eliminate the use of a coating material which is usually employed to coat inside wall of a mould. Further, nonmetallic inclusions and some streak flaws, such as said inclusion, sand seams and the like are reduced. Following table 1 shows comparison of the above flaws of low carbon killed steel cast by the prior method and by the novel method in ordinary bottom pouring process.

TABLE 1 7 Agent Streak flaws (number of measurement 5) Straw Novel ash refining agent Average number of streak flaws per crn. 11. 3 4. 2 Average length of streak flaws per 100 cm.*, mm-. 10. 6 6. 1 Maximum length, mm 5 4 A method utilizing the novel steel-refining agent for continuous casting will now be described with reference to the accompanying drawing. As is shown, the liquid steel 3 is poured into a continuous casting mold 2 from a tundish 1 through a 0 long tubular nozzle 4 and when the surface of liquid steel reaches a predetermined level in the mold 2, supply of the novel refining agent is commenced. The relationship between the surface of slag layer formed by the refining agent and the nozzle 4 is as shown in the drawing. The poured liquid steel solidifies to form a cast slab. As the melting point of the steel refining agent is low, as soon as it comes to contact with liquid steel it will be melted to cover the surface of said liquid steel to prevent oxidation thereof by the atmosphere. In this case, it is apparently found that the component of said steel-refining agent changes as shown in table 2.

Due to these components, melting point of the refining agent can form a slag on the surface of said liquid steel which can readily adsorb and remove such nonmetallic contaminants as silica, alumina, etc., in liquid steel. The slag thus formed adheres to the surface of cast slab and then is removed from the mould. As a result it is necessary to constantly add the refining agent into said mold a rate of about 0.3 to 1.2 kg. per ton of liquid steel.

Where the novel steel refining agent is employed for the continuous casting process of billets and blooms, surface defects thereof can be greatly reduced. Accordingly, repairing loss resulting from some surface defects can be improved as shown in tables 3 and 4.

TABLE 3.-WEIGHT RATIO Continuous casting of a 115 x 115 mm. billet Repairing loss due to surface defects, percent No refining agent used 4. 2 Used the novel refining agent 0. 3

TABLE 4.WEIGHT RATIO Continuous casting of a 1600 x 200 mm. slab Repairing loss due to surface defects, percent No refining agent used 4. 2 Used the novel refining agent 0. 3

Where the novel steel refining agent is not used, the surface of liquid steel killed by aluminum in mold tends to be oxidized by the atmosphere as above described, serum or other slag is formed which caused surface defects. On the contrary, where use is made of the novel refining agent it can not only absorb such serum or slag but also prevent them from being formed. Accordingly, a use of this invention agent can remarkably improved its operability of said continuous casting process and to reduce repairing loss of material surface, while there are many operational difficulties in ordinary continuous casting process of Al-killed steel by reason that said tundish nozzle has tendency to clog.

When slabs having a width or more than 1,200 mm. are moulded by the continuous casting method, longitudinal cracks are formed on the surface of slabs due to thermal stress. However, when the novel steel refining agent is used, the molten refining agent will enter into the gap between the surface of slab and the inside wall of mold to prevent rapid cooling of the slab so that longitudinal cracks due to said heat stress can be effectively prevented. in the continuous casting of slabs having a width of 1,600 X200 mm. without using the novel refining agent tt was noted that longitudinal cracks occurred at a rate of 10 to 30 percent.

Following examples show preferred mixing rate of the novel steel-refining agent.

Example I: For ordinary steel Portland cement 44; Fluorspar l07r Chamotte brick powder 32'; Soda ash 57: Coke breeze or graphite powder 9% Example 2: For aluminum killed steel Portland cement 44; Fluorspar 20% Chamotte brick powder 227 Soda ash 5'1 Coke breeze 9% Example 3: For aluminum killed steel Portland cement 44% Fluorspar lO'Z Chamotte brick powder 22% Soda ash 51 Coke breeze or graphite powder 9; Borax l0; Example dzFor stainless steel Portland cement 44'} Fluorspar 19'71 Chamotte brick powder 24; Soda ash 81 Coke or graphite powder 57: Example 5: ln addition to compounding agent of Example I; Foaming substance 0.0l to 5% (for example, vermiculite, mordenite and foaming synthetic resin).

What is claimed is:

1. A steel-refining agent which is composed of 35 to 60 percent of Portland cement, 5 to 20 percent offluorspar, 20 to 40 percent of Chamotte powder, 2 to 15 percent of soda ash and 2 to 15 percent of carbon source, wherein more than 50 percent of mixing particles have a diameter of less than 0.044

2. a steel refining agent which is composed of 35 to 60 percent of Portland cement, 5 to 20 percent of fluorspar, 20 to 40 percent of Chamotte powder, 0 to 15 percent of soda ash, 2 to 15 percent of carbon source and 2 to 15 percent of borax, wherein more than 50 percent of mixing particles have a diameter of less than 0.044 mm.

3. The steel-refining agent according to claim 1 wherein said source of carbon is selected from the group which is coke breeze and graphite powder.

4. The steel-refining agent according to claim 2 wherein said source of carbon is selected from the group which is coke breeze and graphite powder.

5. The steel-refining agent according to claim I wherein 0.0] to 5 percent ofa foaming substance is added to.

6. A steel-refining agent having a chemical composition of SiO 34.8%, A1 0 14.4%, CaO 30.6%, CaF 8.0%, Na O 3.2% and C 5.7%. 

2. a steel refining agent which is composed of 35 to 60 percent of Portland cement, 5 to 20 percent of fluorspar, 20 to 40 percent of Chamotte powder, 0 to 15 percent of soda ash, 2 to 15 percent of carbon Source and 2 to 15 percent of borax, wherein more than 50 percent of mixing particles have a diameter of less than 0.044 mm.
 3. The steel-refining agent according to claim 1 wherein said source of carbon is selected from the group which is coke breeze and graphite powder.
 4. The steel-refining agent according to claim 2 wherein said source of carbon is selected from the group which is coke breeze and graphite powder.
 5. The steel-refining agent according to claim 1 wherein 0.01 to 5 percent of a foaming substance is added to.
 6. A steel-refining agent having a chemical composition of SiO2 34.8%, A12O3 14.4%, CaO 30.6%, CaF2 8.0%, Na2O 3.2% and C 5.7%. 